Structure and method to form nanopore

ABSTRACT

A method of fabricating a material having nanoscale pores is provided. In one embodiment, the method of fabricating a material having nanoscale pores may include providing a single crystal semiconductor. The single crystal semiconductor layer is then patterned to provide an array of exposed portions of the single crystal semiconductor layer having a width that is equal to the minimum lithographic dimension. The array of exposed portion of the single crystal semiconductor layer is then etched using an etch chemistry having a selectivity for a first crystal plane to a second crystal plane of 100% or greater. The etch process forms single or an array of trapezoid shaped pores, each of the trapezoid shaped pores having a base that with a second width that is less than the minimum lithographic dimension.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.12/843,228, filed Jul. 26, 2010 the entire content and disclosure ofwhich is incorporated herein by reference.

BACKGROUND

The present disclosure relates to methods of forming structuresincluding porosity, such as fluidic channels.

The use of pore containing materials, such as fluidic channels, is knownfor the treatment and observation of, research on, or even the culturingof living cells. For example, fluidic channels including pores are insome instances suitable for DNA sequencing, and molecular sensors. Porecontaining materials are also suitable for water filtration. Porosifiedsemiconductor materials are one type of material that may be utilized inthe above applications.

SUMMARY

A method of fabricating a material having nanoscale pores is provided.In one embodiment, crystallographic etching methods in combination withthe thickness and the composition of the material containing thenanoscale pores is selected to control the diameter, i.e., width, of thenanoscale pores. In one embodiment, the method of fabricating a materialhaving nanoscale pores may include providing a single crystalsemiconductor layer. The single crystal semiconductor layer can bepatterned to provide an array of exposed portions of the single crystalsemiconductor layer having a first width that is equal to the minimumlithographic dimension. The array of exposed portions of the singlecrystal semiconductor layer can be etched using an etch chemistry havinga selectivity for etching a first crystal plane selective to a secondcrystal plane. The etch process forms an array of trapezoid shapedpores, each of the trapezoid shaped pores having a base with a secondwidth that is less than the minimum lithographic dimension.

In another embodiment, the method of fabricating a material havingnanoscale pores may include providing a semiconductor on insulator (SOI)substrate, wherein the semiconductor on insulator substrate includes asingle crystal semiconductor layer on a dielectric layer. The dielectriclayer is present on a base semiconductor layer. The single crystalsemiconductor layer is patterned to provide an array of exposed portionsof the single crystal semiconductor layer having a first width that isequal to the minimum lithographic dimension. The array of exposedportions of the single crystal semiconductor layer is then etched usingan etch chemistry that etches a first crystal plane of the singlecrystal semiconductor layer selective to a second crystal plane of thesingle crystal semiconductor layer. The etch process that forms thearray of trapezoid shaped pores terminates on the dielectric layer. Eachof the trapezoid shaped pores have a base with a second width that isless than the minimum lithographic dimension. The etch process mayterminate on the dielectric layer. The dielectric layer may then beetched to provide a fluidic channel between at least two pores of thearray of trapezoid shaped pores.

In another aspect, a structure is provided including an array ofnanopores formed in a single crystal semiconductor material. Eachnanopore of the array of nanopores has a trapezoid shaped geometry. Thediameter at a first end of each of the nanopores in the array ofnanopores is greater than the minimum lithographic dimension. Thediameter at a second end of each of the nanopores in the array ofnanopores is less than the minimum lithographic dimension.

DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, wherein like referencenumerals denote like elements and parts, in which:

FIG. 1 is a side cross-sectional view depicting one embodiment of asemiconductor substrate, i.e., semiconductor on insulator (SOI)substrate, including at least a single crystal semiconductor layeroverlying a dielectric layer, as used in accordance with the presentdisclosure.

FIG. 2 is a side cross-sectional view depicting patterning the singlecrystal semiconductor layer to provide an array of exposed portions ofthe single crystal semiconductor layer, in which each of the exposedportions of the single crystal semiconductor layer has a first widththat is equal to or greater than a minimum lithographic dimension, inaccordance with one embodiment of the present disclosure.

FIG. 3A is a side cross-sectional view depicting etching the array ofexposed portions of the single crystal semiconductor layer using an etchchemistry having a selectivity for a first crystal plane of the singlecrystal semiconductor layer to a second crystal plane of single crystalsemiconductor layer, wherein the etch process forms an array oftrapezoid shaped pores, each of the trapezoid shaped pores having a basewith a second width that is less than the minimum lithographicdimension, in accordance with one embodiment of the present disclosure.

FIG. 3B is a side cross sectional view of one embodiment of a trapezoidshaped nanopore, in which the width of the base of the trapezoid shapednanopore is related to the height of the trapezoid shaped nanopore.

FIG. 4 is a side cross-sectional view depicting etching the dielectriclayer to provide a fluidic channel between at least two trapezoid shapedpores of the array of trapezoid shaped pores, in accordance with oneembodiment of the present disclosure.

FIG. 5 is a side cross-sectional view depicting etching the dielectriclayer to provide two fluidic channels, wherein each fluidic channel isbetween at least two trapezoid shaped pores of the array of trapezoidshaped pores, in accordance with another embodiment of the presentdisclosure.

FIG. 6 is a side cross-sectional view depicting etching the dielectriclayer and the base semiconductor substrate to provide a fluidic channel,in accordance with another embodiment of the present disclosure.

FIG. 7 depicts one embodiment of a fluidic channel 100E being utilizedto provide a molecular solution, in accordance with another embodimentof the present disclosure.

DETAILED DESCRIPTION

Detailed embodiments of the present disclosure are disclosed herein;however, it is to be understood that the disclosed embodiments aremerely illustrative of the present disclosure that may be embodied invarious forms. In addition, each of the examples given in connectionwith the various embodiments of the present invention are intended to beillustrative, and not restrictive. Further, the figures are notnecessarily to scale, some features may be exaggerated to show detailsof particular components. Therefore, specific structural and functionaldetails disclosed herein are not to be interpreted as limiting, butmerely as a representative basis for teaching one skilled in the art tovariously employ the present invention.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed. For purposes of the description hereinafter, the terms“upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”,“bottom”, and derivatives thereof shall relate to the invention, as itis oriented in the drawing figures. The terms “overlying”, “atop”,“positioned on” or “positioned atop” means that a first element, such asa first structure, is present on a second element, such as a secondstructure, wherein intervening elements, such as an interface structure,e.g. interface layer, may be present between the first element and thesecond element. The term “direct contact” means that a first element,such as a first structure, and a second element, such as a secondstructure, are connected without any intermediary conducting, insulatingor semiconductor layers at the interface of the two elements.

In one embodiment, a method of forming a nanopore array is provided, ineach pore of the nanopore array has a trapezoid shaped cross section.The term “nanopore” denotes an opening having a maximum dimension, e.g.,radius, that is equal to 100 nm or less. The term “trapezoid-shaped”means a four-sided figure with one pair of parallel sides. In oneembodiment, the trapezoid shaped nanopore has the geometry of anisosceles trapezoid, in which the non-parallel sides and base angles ofthe trapezoid are equal.

In one embodiment, the width of the trapezoid shaped nanopore is lessthan the minimum lithographic dimension. The “minimum lithographicdimension” means the smallest dimension obtainable by lithography. Insome examples, the minimum lithographic dimension that a projectionsystem can print is given approximately by:

CD=k ₁·(λ/NA)

-   -   CD is the minimum lithographic dimension    -   k₁ is a coefficient that encapsulates process-related factors        (typically equals 0.4)    -   λ is the wavelength of light    -   NA is the numerical aperture of the lens of the photolithography        device.

In one embodiment, the longer side, i.e., first width, of the parallelsides of the trapezoid shaped nanopore has a dimension that is equal toor greater than the minimum lithographic dimension, and the shorterside, i.e., second width, of the parallel sides of the trapezoid shapednanopore that is less than the minimum lithographic dimension.Typically, the minimum lithographic dimension ranges from 15 nm to 20nm. In one embodiment, pore openings of nanoscale dimension are providedby a method that employs single crystal semiconductor materials incombination with crystalline etching, as depicted in FIGS. 1-3.

FIG. 1 illustrates one embodiment of a substrate 5, i.e., semiconductoron insulator (SOI) substrate, which is suitable for forming a trapezoidshaped nanopore array. The substrate 5 may include at least a singlecrystal semiconductor layer 20 overlying a dielectric layer 15. A basesemiconductor substrate 10 may be present underlying the dielectriclayer 15.

The single crystal semiconductor layer 20 may comprise any singlecrystal semiconducting material including, but not limited to, Si,strained Si, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs,AlAs and InP, or any combination thereof. A single crystal semiconductormaterial is a crystalline solid in which atoms are arranged following aspecific pattern throughout the entire piece of the material, i.e., along-range order exists throughout. In contrast, a polycrystallinematerial is a material in which a long-range order exists only within aportion of the grains, wherein the grains are randomly connected to forma solid. In a polycrystalline material there is no preferentialextension of the single-crystal within the grain in any direction. Incontrast to polycrystalline and single crystal materials, an amorphousmaterial is a non-crystalline solid with no periodicity and nolong-range order at all.

The single crystal semiconductor layer 20 may be thinned to a desiredthickness by planarization, grinding, wet etch, dry etch, or anycombination thereof. One method of thinning the single crystalsemiconductor layer 20 is to oxidize the Si by a thermal dry or wetoxidation process, and then wet etch the oxide layer using ahydrofluoric acid mixture. This process can be repeated to achieve thedesired thickness. In one embodiment, the single crystal semiconductorlayer 20 has a thickness ranging from 10.0 nm to 100.0 nm. In anotherembodiment, the single crystal semiconductor layer 20 has a thicknessranging from 20.0 nm to 90.0 nm. In yet another embodiment, the singlecrystal semiconductor layer 20 has a thickness ranging from 30.0 nm to80.0 nm. In one embodiment, the single crystal semiconductor layer 20 isdoped with a p-type dopant or an n-type dopant. As used herein, “n-type”refers to the addition of impurities that contributes free electrons toan intrinsic semiconductor. In a silicon containing substrate examplesof n-type dopants, i.e., impurities, include but are not limited toantimony, arsenic and phosphorous. In one embodiment, a single crystalsemiconductor layer 20 that is doped with an n-type dopant, the n-typedopant is present in a concentration ranging from 1×10¹⁵ atoms/cm³ to1×10²² atoms/cm³. In another embodiment, the single crystalsemiconductor layer that is doped with an n-type dopant has an n-typedopant concentration ranging from 1×10¹⁷ atoms/cm³ to 1×10²⁰ atoms/cm³.As used herein, a “p-type” refers to the addition of trivalentimpurities to an intrinsic semiconductor that creates deficiencies ofvalence electrons. In one example, the addition of boron, aluminum, orgallium to a type IV semiconductor, such as Si, creates deficiencies ofvalence electrons. In one embodiment, a single crystal semiconductorlayer 20 that is doped with a p-type dopant, the p-type dopant ispresent in a concentration ranging from 5×10¹⁵ atoms/cm³ to 5×10²¹atoms/cm³. In another embodiment, the single crystal semiconductor layer20 is doped with a p-type dopant that is present in a concentrationranging from 1×10¹⁶ atoms/cm³ to 1×10²⁰ atoms/cm³.

The dielectric layer 15 that can be present underlying the singlecrystal semiconductor layer 20 and atop the base semiconductor substrate10 may be formed by implanting a high-energy dopant into the substrate 5and then annealing the structure to form a buried oxide layer, i.e.,dielectric layer 15. In another embodiment, the dielectric layer 15 maybe deposited or grown prior to the formation of the single crystalsemiconductor layer 20. In yet another embodiment, the substrate 5 maybe formed using wafer-bonding techniques, where a bonded wafer pair isformed utilizing glue, adhesive polymer, or direct bonding.

FIG. 2 depicts one embodiment of patterning the single crystalsemiconductor layer 20 to provide an array of exposed portions 21 of thesingle crystal semiconductor layer 20. Each of the exposed portions 21of the single crystal semiconductor layer 20 has a first width W1 thatis equal to or greater than a minimum lithographic dimension. Theminimum lithographic dimension may vary with the photolithographyapparatuses being used to form the etch mask 30, but typically rangesfrom 15 nm to 20 nm. In one embodiment, the width, i.e., first width W1,of each of the exposed portions 21 of the single crystal semiconductorlayer 20 is greater than 20 nm. For example, the width, i.e., firstwidth W1, of each of the exposed portions 21 of the single crystalsemiconductor layer 20 may range from 20 nm to 100 nm. In anotherexample, the width, i.e., first width W1, of each of the exposedportions 21 of the single crystal semiconductor layer 20 may range from25 nm to 80 nm.

In one embodiment, the patterning of the single crystal semiconductorlayer 20 to provide an array of exposed portions 21 of the singlecrystal semiconductor layer 20 includes depositing a photoresist layeron the single crystal semiconductor layer 20, and exposing thephotoresist layer to radiation to provide a pattern corresponding to theunderlying portions of the single crystal semiconductor layer 20 thatbecomes the exposed portions 21 of the single crystal semiconductorlayer 20. Following application of the radiation, the irradiatedportions of the photoresist layer are developed utilizing a resistdeveloper to provide a first etch mask 30 having openings 22 definingthe exposed portions 21 of the single crystal semiconductor layer 20.

In one embodiment, a hardmask (not shown) may be used to define theexposed portions 21 of the single crystal semiconductor layer 20. Thehardmask may be formed by depositing a dielectric hardmask material,like SiN or SiO₂, atop the single crystal semiconductor layer 20 andthen applying a photoresist pattern to the dielectric hardmask materialusing a lithography process steps. The photoresist pattern is thentransferred into the hardmask material using a dry etch process formingthe hardmask.

FIG. 3 depicts one embodiment of etching the array of exposed portions21 of the single crystal semiconductor layer 20. The etch chemistry foretching the array of exposed portions 21 of the single crystalsemiconductor layer 20 may have a selectivity for a first crystal planeof the single crystal semiconductor layer 20 to a second crystal planeof single crystal semiconductor layer 20. In one embodiment, the etchprocess forms an array of trapezoid shaped pores 35. The term “array”denotes a plurality of trapezoid shaped pores 35. In one embodiment, thearray of trapezoid shaped pores 35 includes a concentration of trapezoidshaped pores 35 that ranges from 100 pores/cm³ to 10¹⁰ pores/cm³. Inanother embodiment, the array of trapezoid shaped pores 35 includes aconcentration of trapezoid shaped pores 35 that ranges from 10000pores/cm³ to 10⁶ pores/cm³. In yet another embodiment, the array oftrapezoid shaped pores 35 includes a concentration of trapezoid shapedpores 35 that ranges from 10 pores/cm³ to 100 pores/cm³. In anotherembodiment, a single trapezoid shaped nanopore 35 may be provided forDNA sequencing.

The array of exposed portions 21 of the single crystal semiconductorlayer 20 may be etched using a selective crystallographic etchingmethod. A crystallographic etching method uses an etch chemistry havinga selectivity for a first crystal plane of the single crystalsemiconductor layer 20 to a second crystal plane of the single crystalsemiconductor layer 20. As used herein, the terms “selective” and“selectivity” in reference to a material removal process denotes thatthe rate of material removal for a first material is greater than therate of removal for at least another material of the structure to whichthe material removal process is being applied. For example, in oneembodiment, the selectivity for removing the first crystal plane to thesecond crystal plane is greater than 100%. In another embodiment, theselectivity for removing the first crystal plane to the second crystalplane is greater than 200% and less than 600%. In yet anotherembodiment, the selectivity for removing the first crystal plane to thesecond crystal plane is greater than 400. The crystallographic etch mayalso be selective to the material of the dielectric layer 15. In thisembodiment, the crystallographic etch terminates on the dielectric layer15.

In one embodiment, in which the single crystal semiconductor layer 20 isa silicon-containing material, the first crystal plane is <100> and thesecond crystal plane is <111>, in which the first crystal plane isetched selectively to the second crystal plane. The <100> crystal planeof the single crystal semiconductor layer 20 extends along a directionthat is parallel to the upper surface of the single crystalsemiconductor layer 20.

In one embodiment, in which the single crystal semiconductor layer 20 isa silicon-containing material, such as silicon, the selectivity of thecrystallographic etch provides an isosceles trapezoid shaped pore 35, inwhich the angle, i.e., acute angle, at the intersection of the sidewallS1 of the isosceles trapezoid shaped pore 35 and the upper surface ofthe dielectric layer 15 is approximately 54 degrees. In one embodiment,in which the second crystal plane is <111>, and the etchant etches the<100> crystal plane of the single crystal semiconductor layer 20selective to the <111> crystal plane, the sidewall Si of the isoscelestrapezoid shaped pore 35 extends along the <111> direction. It is notedthat other materials may be provided for the single crystalsemiconductor layer 20, and that the present disclosure should not belimited to the above example, in which the single crystal semiconductorlayer 20 is composed of silicon. Other materials that can becrystallographically etched to provide a trapezoid shaped pore 35 arewithin the scope of the methods and structures disclosed herein. Forexample, in some embodiments, the single crystal semiconductor layer 20that is crystallographically etched to provide the trapezoid shaped pore35 may include, but is not limited to Si, Ge, SiGe, GaAs, InAs, AlAs orcombinations and multi-layers thereof.

Referring to FIG. 3A, and in one embodiment, the diameter, i.e., firstwidth W1, of a first opening at a first end, i.e., upper surface, of thetrapezoid shaped nanopore 35 is greater than the minimum lithographicdimension, and the diameter, i.e., second width W2, of a second openingat a second end of the trapezoid shaped nanopores 35 is less than theminimum lithographic dimension. The first and second openings arepositioned on opposing sides of the trapezoid shaped nanopore 35 and arein fluid communication. In one example, the opening at the first end ofthe trapezoid shaped nanopore has a width, i.e., diameter, that is equalto the width W2 defined by the openings in the etch mask 30. In someinstances, because the openings in the etch mask 30 are defined byphotolithography, the minimum width, i.e., diameter, of the firstopening may be equal to the minimum lithographic dimension or may begreater than the minimum lithographic dimension.

In some embodiments, the crystallographic etch that is applied to theexposed portions 21 of the single crystal semiconductor layer 30 resultsin a tapered pore (trapezoid shaped pore 35), wherein the width of thetrapezoid shaped pore 35 reduces with in increasing depth into thesingle crystal semiconductor layer 20 from the first opening of thetrapezoid shaped pore 35. Therefore, because the width of the trapezoidshaped pore 35 reduces with increasing depth into the single crystalsemiconductor layer 20, the diameter, i.e., second width, of the secondopening at the base of the trapezoid shaped pore 35 is less than theminimum lithographic dimension. FIG. 3B illustrates that as thethickness of the single crystal semiconductor layer 20 increases and theheight of the trapezoid shaped nanopore increases, e.g., H1<H2<H3, thewidth of second opening at the base of the trapezoid shaped pore 35decreases, e.g., Wa>Wb>Wc.

Referring to FIGS. 3A, one example of an etchant suitable forcrystallographic etching of the single crystal semiconductor layer 20 ispotassium hydroxide (KOH). Potassium hydroxide (KOH) etches the <100>plane of silicon selective to the <111> plane of silicon. In oneembodiment, potassium hydroxide (KOH) may provide an etch selectivity of400 between the <100> and <111> crystal planes. Other examples ofetchants that may provide isosceles trapezoid shaped pore 35 includeethylene diamine and pyrocatechol (EDP).

Referring to FIG. 3A, the base of the trapezoid shaped pore 35 has awidth, i.e., second width W2, that is less than the first width W1 atthe upper surface of the trapezoid shaped pore 35, and is therefore lessthan the minimum lithographic dimension. In one embodiment, the width ofthe base, i.e., second width W2, of the trapezoid shaped pore 35 may bedictated by selecting the thickness T1 of the single crystalsemiconductor layer 20 in combination with the material of the singlecrystal semiconductor 20 in combination with the crystalline etchingmethod. In the embodiments, in which the angle α, i.e., acute angle, atthe intersection of the sidewall S1 of the isosceles trapezoid shapedpore 35 and the upper surface of the dielectric layer 15 isapproximately 54 degrees, the width of the base, i.e., second width W2,of the trapezoid shaped pore 35 may be dictated by the equation:

W1=W2+(2×T1×COS/SIN 54°)

-   -   W1 is the first width at the upper surface of the trapezoid        shaped pore    -   W2 is the second width at the base of the trapezoid shaped pore    -   T1 is the thickness of the single crystal semiconductor layer        20.

Referring to FIG. 3A, and in one embodiment, each of the trapezoidshaped pores 35 of the array of trapezoid shaped pores 35 has a basewith a second width W2 that is less than the minimum lithographicdimension. In one example, the base of each of the trapezoid shapedpores 35 has a width, i.e., second width W2, ranging from 1 nm to 15 nm.In another example, the base of each of the trapezoid shaped pores 35ranges from 2 nm to 10 nm. In yet another example, the base of each ofthe trapezoid shaped pores 35 ranges from 5 nm to 7 nm. The width, i.e.,first width W1, at the first end, i.e., upper surface, of the firstopening each of the trapezoid shaped pores 35 is greater than 20 nm. Forexample, the width, i.e., first width W1, of each of the first openingto each of the trapezoid shaped pores 35 may range from 21 nm to 100 nm.In another example, the width, i.e., first width W1, of the firstopening to each of the trapezoid shaped pores 35 may range from 25 nm to80 nm.

In one embodiment, the crystallographic etching provides uniformity forthe second width W2 at the second opening of the trapezoid shaped pores35 not previously capable of being produced by prior methods. In oneembodiment, the standard deviation of the second width W2 of the openingat the second end of each trapezoid shaped nanopore 35 of the array oftrapezoid shaped nanopores 35 ranges from 1 to 10. In anotherembodiment, the standard deviation of the second width W2 of the secondend of each trapezoid shaped nanopore 35 of the array of nanopores 35ranges from 1 to 5. In yet another embodiment, the standard deviation ofthe second width W2 of the second end of each trapezoid shaped nanopore35 of the array of nanopores 35 ranges from 1 to 3.

FIG. 4 depicts etching the dielectric layer 15 to provide a fluidicchannel 100A between at least two trapezoid shaped pores 35 of the arrayof trapezoid shaped pores 35. In one embodiment, at least a portion ofthe dielectric layer 15 is removed using an isotropic etch. An isotropicetch process is a material removal process in which the rate of theetching reaction is substantially similar in any direction. The etchprocess may include a plasma etch or a wet etch. The etchant isintroduced to the dielectric layer 15 through the trapezoid shaped pores35. When the buried dielectric layer 15 comprises a silicon oxidedielectric material, the isotropic etchant may include a dilutehydrofluoric acid etchant or a dilute buffered hydrofluoric acidetchant. The present disclosure is not, however, limited to theforegoing materials compositions. The remaining portion of thedielectric layer 15 provides pedestals that support the remainingportions of the single crystal semiconductor layer 20.

In the embodiment depicted in FIG. 4, the fluidic channel 100A includesthree trapezoid shaped pores 35 as an inlet to the fluidic channel 100Aand a single trapezoid shaped pore 35 as the exit of the fluidic channel100A, in which the arrows depict the flow of fluid through the fluidicchannel 100A. FIG. 5 depicts another embodiment of a fluidic channel100B, 100C that may be formed using the above-described method. Morespecifically, the embodiment depicted in FIG. 5 includes two fluidicchannels 100B, 100C separated by a pedestal region 50. Each fluidicchannel 100B, 100C includes a single inlet provided by a trapezoidshaped pore 35 and a single outlet provided by a trapezoid shaped pore35, in which the arrows depict the flow of fluid through the fluidicchannels 100B, 100C.

FIG. 6 depicts another embodiment of a fluidic channel 100D. In thisembodiment, the dielectric layer 15 is removed using an isotropic etch,as depicted in FIG. 4. Following removal of the dielectric layer 15, aportion of the base semiconductor substrate 10 may be removed to providea fluidic channel 100D that extends through the entire semiconductorsubstrate 5. In one embodiment, the base semiconductor substrate 10 maybe removed by an anisotropic etch, such as a reactive ion etch. Ananisotropic etch process is a material removal process in which the etchrate in the direction normal to the surface to be etched is much higherthan in the direction parallel to the surface to be etched. Reactive ionetch is a form of plasma etching, in which the surface to be etched isplaced on the RF powered electrode and takes on a potential thataccelerates an etching species, which is extracted from a plasma,towards the surface to be etched, wherein a chemical etching reactiontakes place in the direction normal to the surface being etched. In oneembodiment, a second etch mask may be provided in direct contact withthe base semiconductor substrate 10 by a patterned photoresist layer.

The fluidic channels 100A, 100B, 100C, 100D of the present disclosuremay be employed in DNA sequencing, molecular sensors, molecular filtersand water treatment. FIG. 7 depicts one embodiment of a fluidic channel100E being utilized to provide a molecular solution. Reference number 55depicts a DNA solution in salt with a concentration gradient. Theconcentration is typically equal to approximately 500 nM. Referencenumber 60 depicts a salt solution. The salt solution is typicallycomposed of 1M KCl/10 nM Tris.Cl. The PH of the solution isapproximately 8.5. In one embodiment, DNA from the DNA solution in salt55 translocate through the trapezoid shaped nanopore 35. In one example,the structure depicted in FIG. 7 leads to 1 translocation per second to2 translocations per second. The arrow depicted in FIG. 7 illustratesthe direction in which the translocations are traveling through thetrapezoid shaped nanopore 35. A bias is applied to the structuredepicted in FIG. 7 to control the translocation rate. The above notedapplications for the fluidic channels 100A, 100B, 100C, 100D, 100E areprovided for illustrative purposes, and are not intended to limit theapplication of the methods and structures disclosed in the presentdisclosure.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

What is claimed is:
 1. A fluidic structure comprising: a single crystal semiconductor material; and an array of nanopores having a trapezoid shaped geometry through the single crystal semiconductor material, wherein a first width at a first end of each nanopore of the array of nanopores is greater than the minimum lithographic dimension, and a second width at a second end of each nanopore of the array of nanopores that is less than the minimum lithographic dimension.
 2. The fluidic structure of claim 1, wherein a standard deviation of the second width of the second end of each nanopore of the array of nanopores ranges from 1 to
 5. 3. The fluidic structure of claim 1, wherein a standard deviation of the second width of the second end of each nanopore of the array of nanopores ranges from 1 to
 3. 4. The fluidic structure of claim 1, wherein a concentration of the array of nanopores ranges from 1000 to 10¹² cm⁻³.
 5. The fluidic structure of claim 1, wherein a concentration of the array of nanopores ranges from 1000 to 10¹⁰ cm⁻³.
 6. The fluidic structure of claim 1, wherein a concentration of the array of nanopores ranges from 10000 to 10¹⁶ cm⁻³.
 7. The fluidic structure of claim 1, wherein a concentration of the array of nanopores ranges from 1000 to 10⁶ cm⁻³.
 8. The fluidic structure of claim 1, wherein the first width ranges from 20 nm to 100 nm, and the second width ranges from 5 nm to 10 nm.
 9. The fluidic structure of claim 1, wherein the first width ranges from 25 nm to 80 nm.
 10. The fluidic channel of claim 1, wherein the second width ranges from 1 nm to 15 nm.
 11. The fluidic channel of claim 1, wherein the second width ranges from 2 nm to 10 nm.
 12. The fluidic structure of claim 1, wherein the minimum lithographic dimension ranges from 15 nm to 20 nm.
 13. The fluidic structure of claim 1, wherein the single crystal semiconductor material comprises Si, strained Si, SiC, SiGe, SiGeC, Si alloys, Ge, Ge alloys, GaAs, InAs, AlAs, InP, or a combination thereof.
 14. The fluidic structure of claim 1, wherein the single crystal semiconductor material comprises a crystal plane selected from the group consisting of: <111>, <100> and a combination thereof.
 15. The fluidic structure of claim 1, wherein the trapezoid shaped geometry is isosceles.
 16. The fluidic structure of claim 15, wherein the sidewall of the trapezoid shaped geometry of each nanopore that is isosceles has a sidewall along a <111> direction. 